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Thread: Lost leg on Delta Transformer?

  1. #21
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    I worry with all the DIY hackwork, there may be additional ground bonds in the building and/or equipment

    250 amp total at 240V is 60 KVA I wouldn't worry too much about a 30 KVA trans on that service, not normally, but with all the hackwork, everything could be loaded on one winding.

    Or maybe one winding is defective, and this place is operating on an open delta, then the trans, or bank of trans has to be derated to 57.7% capacity.

    You are going to end up having to check everything, starting with the transformer windings.
    Proverbs 31;10


  2. #22
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    Nobody who knows what they are doing, even in the slightest way buys single phase equipment for a place with a 3 phase service. For the most part, 3 phase equipment is cheaper to buy. And on the used market most times 3 phase equipment can be had for next to nothing. The 3 phase scares all the DIY guys so it limits the market
    Proverbs 31;10


  3. #23
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    Quote Originally Posted by jim dungar View Post
    Be careful about using terms incorrectly.
    Stop believing what an uninformed layperson tells you, trust your training and the experts on this forum.

    A grounded conductor is not always a neutral.
    Corner grounded 3-phase systems have been used for almost 100yrs. Typically the only special requirement is that 2-pole breakers can not be 'slash rated' (in the Square D world you cannot use a QO220, instead you need a QO220H).

    Corner grounded systems are not necessarily more unsafe than any other system just because they are 240V L-G, after all a center-tapped 240/120V system has one leg that is 208V L-G.
    I guess I was referring to the following link (which was posted earlier in this thread), and others like it: http://www.google.com/url?sa=t&rct=j...zVaRQWqgJFVpbQ

    But I'm beginning to think that the best way to go, is to let a sleeping dog lie and just add another panel off of the corner ground transformer. I can test phases for balance. If I need to upsize the trans, I could just get the same style, and corner ground it as well?

  4. #24
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    Quote Originally Posted by Psychlo View Post
    I guess I was referring to the following link (which was posted earlier in this thread), and others like it: http://www.google.com/url?sa=t&rct=j...zVaRQWqgJFVpbQ

    But I'm beginning to think that the best way to go, is to let a sleeping dog lie and just add another panel off of the corner ground transformer. I can test phases for balance. If I need to upsize the trans, I could just get the same style, and corner ground it as well?
    Well I would get one capable of being hooked up as a high leg 120/240 high leg delta just to leave future options open, BUT I would, for now, connect it as a a corner ground so it fits into the same electrical "footprint"
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  5. #25
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    Quote Originally Posted by Psychlo View Post
    It would take a set of double lugs to come off of the trans again. But I may need to upsize the tranny anyway. It's a 30kVA. I'll have two panels coming off of it - 150amp and 100amp. I don't know the exact connected load, yet.

    In the articles I've been reading, I'm finding that most people are recommending to steer clear of corner ground setups. If I have to change out the tranny anyway, I thought it might be easier (and safer) to switch it over to a more standard scenario. Since the existing loads are all 1-phase, 240v, it wouldn't require rewiring of the branch circuits, right? Or is there a possibility that they tied B-phase to ground at the equipment also?

    As you may have noticed, I'm no transformer wiz. Even so, this whole system seems counter-intuitive. Identifying B-phase as a neutral, even though it is a phase conductor? Seems like we're in the Twilight Zone! But that's just my inexperience talking.
    Jim commented on this already but I will add my $.02.

    You are not identifying the B phase as a neutral, you are identifying it as a grounded conductor, there is a difference. Whenever there is a "neutral" it is usually grounded, so on those systems they are the same conductor.

    As far as changing it to 4 wire delta system, you will need a fourth service conductor, if you don't have breakers on the B phase now you will need overcurrent devices on it after the change. Although there is concern about B phase being bonded someplace besides the service equipment, that is improper installation anyway. Just like other systems the equipment grounding conductor and system grounded conductors are to be separate past the service equipment. If there is a bond past the service and you change this to a 4 wire delta system you will find out quickly which circuits have a ground connection on B phase.

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    Quote Originally Posted by Joethemechanic View Post
    I worry with all the DIY hackwork, there may be additional ground bonds in the building and/or equipment

    250 amp total at 240V is 60 KVA I wouldn't worry too much about a 30 KVA trans on that service, not normally, but with all the hackwork, everything could be loaded on one winding.

    Or maybe one winding is defective, and this place is operating on an open delta, then the trans, or bank of trans has to be derated to 57.7% capacity.

    You are going to end up having to check everything, starting with the transformer windings.
    Agreed.

    But if one winding was defective, wouldn't the voltage readings be different? What would the readings be if it was an open delta?

    After hearing all of you guys, it sounds like the transformer probably is working fine. I'll chat with the owner tomorrow and see why he thinks he lost a leg ten years ago.

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    Quote Originally Posted by Joethemechanic View Post
    I worry with all the DIY hackwork, there may be additional ground bonds in the building and/or equipment
    There has been no mention form the OP about hack work at this site. From the discussion so far, a layperson incorrectly described a grounded systems as having an open phase. Nothing else seems to be amiss.

    250 amp total at 240V is 60 KVA I wouldn't worry too much about a 30 KVA trans on that service, not normally, but with all the hackwork, everything could be loaded on one winding.
    This is does not appear to be a service. I believe it has been described as a customer owned 30kVA transformer.
    Just because you can, doesn't mean you should.

  8. #28
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    Open Delta
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    Proverbs 31;10


  9. #29
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    Another view
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    Proverbs 31;10


  10. #30
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    Quote Originally Posted by Psychlo View Post
    This is an older fab shop that has had a lot of mickey-mouse repairs and add-ons over the years.
    Jim,

    This says DIY hackwork to me
    Proverbs 31;10


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